1. Field of the Invention
The present invention relates to an inferior-and-superior-limb blood-pressure-index measuring apparatus for measuring an inferior-and-superior-limb blood-pressure index of a living subject.
2. Related Art Statement
An inferior-and-superior-limb blood-pressure index is generally known as a ratio of a blood pressure of a superior limb of a living subject to a blood pressure of an inferior limb of the subject, or a ratio of the blood pressure of the inferior limb to that of the superior limb. Respective systolic blood pressures of the inferior and superior limbs are generally used as the respective blood pressures of those limbs. In addition, generally, an ankle is selected as the inferior limb and an upper arm is selected as the superior limb, so that an ankle-and-upper-arm blood-pressure index is determined as the inferior-and-superior-limb blood-pressure index. The inferior-and-superior-limb blood-pressure index represented by the ankle-and-upper-arm blood-pressure index is used as an index useful for making a diagnosis about stenosis or obliteration caused by atherosclerosis.
Since the inferior-and-superior-limb blood-pressure index is a simple ratio, i.e., a ratio of one of inferior-limb blood pressure and superior-limb blood pressure to the other, a diagnosis made based on the index is largely influenced by a small change of the inferior-limb and/or superior-limb blood pressure. Meanwhile, blood pressure of a living person may largely change in a short time. For example, even when the person is resting, his or her blood pressure may physiologically change by more than 20 mmHg in 10 seconds. Therefore, if an inferior-limb blood pressure and a superior-limb blood pressure are measured at different times, blood pressure of the person may largely change between those times. Thus, measurement of a reliable inferior-and-superior-limb blood-pressure index requires that an inferior-limb blood pressure and a superior-limb blood pressure be measured at substantially the same time.
Japanese Patent No. 3,027,751 or its corresponding U.S. Pat. No. 6,332,869 discloses an ankle-and-upper-arm blood-pressure-index measuring apparatus which measures an ankle systolic blood pressure and an upper-arm systolic blood pressure at substantially the same time, and calculates an ankle-and-upper-arm blood-pressure index based on the thus measured ankle and upper-arm systolic blood pressure. The disclosed apparatus measures the ankle and upper-arm systolic blood pressure at substantially the same time, by carrying out two blood-pressure measuring operations. More specifically described, the apparatus includes an ankle cuff wound around an ankle and an upper-arm cuff wound around an upper arm, determines the ankle and upper-arm systolic blood pressure obtained in the first blood-pressure measuring operation, as estimated ankle and upper-arm systolic blood pressure, respectively, and controls, in the second blood-pressure measuring operation, the respective pressures of the ankle cuff and the upper-arm cuff, such that the respective pressures of the ankle cuff and the upper-arm cuff become equal to the estimated ankle and upper-arm systolic blood pressure, respectively, at substantially the same time.
However, since the ankle-and-upper-arm blood-pressure-index measuring apparatus disclosed in the above-identified document needs to carry out two blood-pressure measuring operations, it takes a long time to measure the blood-pressure index and a patient feels much discomfort caused by pressing of the cuffs.
It is therefore an object of the present invention to provide an inferior-and-superior-limb blood-pressure-index measuring apparatus which can measure, in a single blood-pressure measuring operation, an inferior-limb systolic blood pressure and a superior-limb systolic blood pressure of a patient, at substantially the same time, and thus can measure an inferior-and-superior-limb blood-pressure index of the patient in a short time with reduced discomfort felt by the patient.
The above object has been achieved by the present invention. According to the present invention, there is provided an apparatus for measuring an inferior-and-superior-limb blood-pressure index of a living subject, comprising an inferior-limb blood-pressure measuring device which includes an inferior-limb cuff adapted to be wound around a portion of an inferior limb of the subject and measures a systolic blood pressure of the inferior limb based on a heartbeat-synchronous signal which is obtained from the subject when a pressure of the inferior-limb cuff is decreased after the pressure of the inferior-limb cuff is increased up to an estimated pressure higher than a systolic blood pressure of the portion of the inferior limb; a superior-limb blood-pressure measuring device which includes a superior-limb cuff adapted to be wound around a portion of a superior limb of the subject and measures a systolic blood pressure of the superior limb based on a heartbeat-synchronous signal which is obtained from the subject when a pressure of the superior-limb cuff is decreased after the pressure of the superior-limb cuff is increased up to a pressure higher than an estimated systolic blood pressure of the portion of the superior limb; an inferior-and-superior-limb-blood-pressure-index determining means for determining the inferior and-superior-limb blood-pressure index of the subject, based on the systolic blood pressure of the inferior limb measured by the inferior-limb blood-pressure measuring device and the systolic blood pressure of the superior limb measured by the superior-limb blood-pressure measuring device; an estimated-inferior-limb-systolic-blood-pressure determining means for determining the estimated systolic blood pressure of the portion of the inferior limb based on a heartbeat-synchronous signal which is obtained from the subject when the pressure of the inferior-limb cuff is increased; an estimated-superior-limb-systolic-blood-pressure determining means for determining the estimated systolic blood pressure of the portion of the superior limb based on a heartbeat-synchronous signal which is obtained from the subject when the pressure of the superior-limb cuff is increased; and a cuff-pressure control means for controlling at least one of the respective pressures of the inferior-limb cuff and the superior-limb cuff, such that when the respective pressures of the inferior-limb cuff and the superior-limb cuff are decreased, the respective pressures of the inferior-limb cuff and the superior-limb cuff become equal to the respective estimated systolic blood pressures of the inferior limb and the superior limb, at a same time.
According to this invention, the estimated-inferior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the inferior limb based on the heartbeat-synchronous signal obtained when the pressure of the inferior-limb cuff is increased, and the estimated-superior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the superior limb based on the heartbeat-synchronous signal obtained when the pressure of the superior-limb cuff is increased. When the respective pressures of the inferior-limb and superior-limb cuffs are slowly decreased after being increased, the cuff-pressure control means controls at least one of the respective pressures of the inferior-limb cuff and the superior-limb cuff, such that the respective pressures of the inferior-limb cuff and the superior-limb cuff become equal to the respective estimated systolic blood pressures of the inferior limb and the superior limb, at the same time. Thus, the present apparatus can measure, in the single blood-pressure measuring operation, the inferior-limb systolic blood pressure and the superior-limb systolic blood pressure, at substantially the same time.
Here, preferably, the cuff-pressure control means comprises a pressure-increase control means for increasing the pressure of the inferior-limb cuff from a pressure which is estimated to be lower than a diastolic blood pressure of the portion of the inferior limb, and increasing the pressure of the superior-limb cuff from a pressure which is estimated to be lower than a diastolic blood pressure of the portion of the superior limb, wherein the apparatus further comprises a diastolic-and-mean-blood-pressure measuring device which measures a diastolic blood pressure and a mean blood pressure of the inferior limb based on the heartbeat-synchronous signal obtained from the subject when the pressure of the inferior-limb cuff is increased by the pressure-increase control means, and measures a diastolic blood pressure and a mean blood pressure of the superior limb based on the heartbeat-synchronous signal obtained from the subject when the pressure of the superior-limb cuff is increased by the pressure-increase control means; an inferior-limb-pulse-wave detecting device which detects an inferior-limb pulse wave that is an oscillation of the pressure of the inferior-limb cuff a superior-limb-pulse-wave detecting device which detects a superior-limb pulse wave that is an oscillation of the pressure of the superior-limb cuff; an inferior-limb-pulse-wave-magnitude determining means for determining a minimal magnitude, an area-gravity-center magnitude, and a maximal magnitude of at least one heartbeat-synchronous pulse of the inferior-limb pulse wave detected by the inferior-limb-pulse-wave detecting device in a state in which the pressure of the inferior-limb cuff is kept at a pressure which is estimated to be lower than a mean blood pressure of the portion of the inferior limb; and a superior-limb-pulse-wave-magnitude determining means for determining a minimal magnitude, an area-gravity-center magnitude, and a maximal magnitude of at least one heartbeat-synchronous pulse of the superior-limb pulse wave detected by the superior-limb-pulse-wave detecting device in a state in which the pressure of the superior-limb cuff is kept at a pressure which is estimated to be lower than a mean blood pressure of the portion of the superior limb, and wherein the estimated-inferior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the portion of the inferior limb based on the diastolic blood pressure and the mean blood pressure of the inferior limb, measured by the systolic-and-mean-blood-pressure measuring device, and the minimal magnitude, the area-gravity-center magnitude, and the maximal magnitude of the inferior limb pulse wave, determined by the inferior-limb-pulse-wave-magnitude determining means, and the estimated-superior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the portion of the superior limb based on the diastolic blood pressure and the mean blood pressure of the superior limb, measured by the systolic-and-mean-blood-pressure measuring device, and the minimal magnitude, the area-gravity-center magnitude, and the maximal magnitude of the superior-limb pulse wave, determined by the superior-limb-pulse-wave-magnitude determining means.
According to this feature, when the pressure-increase control means slowly increases the respective pressures of the inferior-limb cuff and the superior-limb cuff, the inferior-limb-pulse-wave detecting device detects the inferior-limb pulse wave, the superior-limb-pulse-wave detecting device detects the superior-limb pulse wave, and the diastolic-and-mean-blood-pressure measuring device measures the diastolic and mean blood pressure of the inferior limb, and the diastolic and mean blood pressure of the superior limb. And, the estimated-inferior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the inferior limb based on the diastolic and mean blood pressure of the inferior limb, actually measured by the systolic-and-mean-blood-pressure measuring device, and a minimal magnitude, an area-gravity-center magnitude, and a maximal magnitude of the inferior-limb pulse wave actually detected, and the estimated-superior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the superior limb based on the diastolic and mean blood pressure of the superior limb, actually measured by the systolic-and-mean-blood-pressure measuring device, and a minimal magnitude, an area-gravity-center magnitude, and a maximal magnitude of the superior-limb pulse wave actually detected. Therefore, the present apparatus can determine, with high accuracy, the estimated systolic blood pressure of the inferior limb and the estimated systolic blood pressure of the superior limb, and accordingly can measure, in the single blood-pressure measuring operation, the inferior-limb systolic blood pressure and the superior-limb systolic blood pressure, at accurately the same time.
In addition, preferably, the inferior-and-superior-limb blood-pressure-index measuring apparatus further comprises a mean-blood-pressure measuring device which measures a mean blood pressure of the inferior limb based on the heartbeat-synchronous signal obtained from the subject when the pressure of the inferior-limb cuff is increased, and measures a mean blood pressure of the superior limb based on the heartbeat-synchronous signal obtained from the subject when the pressure of the superior-limb cuff is increased, wherein the estimated-inferior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the portion of the inferior limb based on the heartbeat-synchronous signal obtained from the subject when the pressure of the inferior-limb cuff is increased and before the mean blood pressure of the inferior limb is measured by the mean-blood-pressure measuring device, wherein the estimated-superior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the portion of the superior limb based on the heartbeat-synchronous signal obtained from the subject when the pressure of the superior-limb cuff is increased and before the mean blood pressure of the superior limb is measured by the mean-blood-pressure measuring device, and wherein the cuff-pressure control means comprises a pressure-increase control means for increasing, at a first rate, the pressure of the inferior-limb cuff from a pressure which is estimated to be lower than a diastolic blood pressure of the portion of the inferior limb, and increasing, at a second rate, the pressure of the superior-limb cuff from a pressure which is estimated to be lower than a diastolic blood pressure of the portion of the superior limb, and further increasing, at a third rate higher than the first rate, the pressure of the inferior-limb cuff to a first pressure-decrease starting pressure determined based on the estimated systolic blood pressure of the inferior limb determined by the estimated-inferior-limb-systolic-blood-pressure determining means, when the mean blood pressure of the inferior limb is measured by the mean-blood-pressure measuring device, at a time later than a time when the mean blood pressure of the superior limb is measured by the mean-blood-pressure measuring device, and further increasing, at a fourth rate higher than the second rate, the pressure of the superior-limb cuff to a second pressure-decrease starting pressure determined based on the estimated systolic blood pressure of the superior limb determined by the estimated-superior-limb-systolic-blood-pressure determining means, when the mean blood pressure of the superior limb is measured at a time later than a time when the mean blood pressure of the inferior limb is measured.
According to this feature, when the pressure-increase control means slowly increases the respective pressures of the inferior-limb cuff and the superior-limb cuff, the mean-blood-pressure measuring device measures the mean blood pressure of the inferior limb and the mean blood pressure of the superior limb. The estimated-inferior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the inferior limb based on the heartbeat-synchronous signal obtained before the mean blood pressure of the inferior limb is measured, and the estimated-superior-limb-systolic-blood-pressure determining means determines the estimated systolic blood pressure of the superior limb based on the heartbeat-synchronous signal obtained before the mean blood pressure of the superior limb is measured. And, the pressure-increase control means further increases, more quickly, the pressure of the inferior-limb cuff to a pressure-decrease starting pressure determined based on the estimated systolic blood pressure of the inferior limb, when the mean blood pressure of the inferior limb is measured at a time later than a time when the mean blood pressure of the superior limb is measured, and further increases, more quickly, the pressure of the superior-limb cuff to a pressure-decrease starting pressure determined based on the estimated systolic blood pressure of the superior limb, when the mean blood pressure of the superior limb is measured at a time later than a time when the mean blood pressure of the inferior limb is measured. Thus, the present apparatus can increase the respective pressures of the inferior-limb cuff and the superior-limb cuff, to the respective pressure-decrease starting pressures, in a shorter time than a time in which the respective pressures of the inferior-limb cuff and the superior-limb cuff are slowly increased till respective systolic blood pressures of the inferior and superior limbs are measured so that those measured systolic blood pressures of the inferior and superior limbs are used as respective estimated systolic blood pressures of the inferior and superior limbs.